Techniques for analyzing lead condition in visible, infrared and microwave satellite imagery

The condition of a lead or polynya, whether open, partially refrozen, or completely ice covered, is extremely important from many points of view. From a meteorological and climatological perspective the moisture and heat flux resulting from air and sea interaction over leads during cold weather periods is crucial. Enormous cloud plumes have been observed emanating from relatively small openings in leads and polynyas. Modeling studies have shown that plume development is extremely sensitive to changes in humidity, air temperature, and the nature of near‐surface atmospheric lapse rates. The studies indicate that plumes can exist, even in the refreezing process, until the new ice becomes sufficiently thick so that its temperature approaches the temperature of the surrounding ice. Heat balance studies for modeling the arctic environment depend upon knowledge of such distinctions for accurate assessment of the radiation balance over the area at any given time. This paper describes a new visible channel differencing technique shown to have some capabilities in distinguishing between open and refrozen leads and, in larger leads, distinguishing the part that is open from that which is partially or newly refrozen. Output from this technique is correlated with infrared data in two examples over the Beaufort Sea and in a polynya example with additional microwave data over the Laptev Sea. Although in situ evidence for direct documentation of lead condition is limited, the existence of cloud plumes emanating from open leads provides some verification and establishment of remote sensing parameters indicative of an open or closed condition. A logical consistency of values from independent sensors over varying conditions of open water, mixed ice and water, new ice, and first or multiyear ice also provides contributing remote sensing evidence of lead condition.